've used intersurf to show the interface area between two different protein sub-units. I'm attaching an image.

Is it possible to increase the transparency of the interface area shown in red? I found no way to do so.

Many thanks in advance for any suggestions

Regards

George

PS. No attachment as it is 33.5 Mb. By the way, is there a way to reduce the size of tiff images without compromising the quality?